Reprovisioning monitor

ABSTRACT

A device for enabling automatic restoration of network access for user lines within a communication system. The user lines interface with groups of transmission lines that include dedicated transmission lines which are connected to the user lines, idle transmission lines and reserved transmission lines. The device includes a line manager that makes a number of transmission lines among the groups of transmission lines available for user lines which have a dedicated transmission line in a group of transmission lines that fails and a reprovisioning element that couples each of such user lines to a respective available transmission line. The device may also include a monitor that delays the coupling of such user lines if a sufficient number of transmission lines are not available.

Related applications entitled "AN IMPROVED DIGITAL LOOP CARRIER SYSTEM";"A METHOD OF MANAGING DIGITAL SIGNAL CARRYING FACILITIES", applicationSer. No. 08/625,184; and "A METHOD OF PROVIDING CONTINUAL NETWORK ACCESSFOR SUBSCRIBER COMMUNICATION LINES", application Ser. No. 08/625,185 nowabandoned, by the same inventor, are being filed on the same dayherewith and are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates generally to telephone communicationsystems and more particularly, to a device adapted to be utilized in adigital telephone system for enabling the automatic restoration ofnetwork access for user lines in the event of a failure.

BACKGROUND OF THE INVENTION

In modern telephone networks the use of digital technology has becomewidespread. Utilizing digital technology in telephone networks has anumber of advantages. One advantage is that the digital transmission ofdata is less susceptible to noise, which improves the quality of thetransmission. While another advantage is that the digital format isideal for being implemented on solid state technology such as integratedcircuits. This is significant because most of the developments intechnology has been in this area.

In order to exploit the advantages of digital technology, new techniquesand equipment had to be developed. These new developments have includednew modulation techniques, digital switches and various digitalinterfaces.

An example of a system utilized in digital telephone networks is shownin FIG. 1, which is known as a Digital Loop Carrier or an IntegratedDigital Loop Carrier (IDLC) system 10. The IDLC system 10 is utilized tocouple subscriber lines 22, 24, 26, 28 to a switching system 12, such asan EWSD® switching system, which routes calls from the subscriber lines22, 24, 26, 28 to other parts of the phone network.

The IDLC system 10 includes a remote digital terminal (RDT) 30 whichinterfaces the subscriber lines 22, 24, 26, 28 to a number of 1.544 MPBShighways 14,18. The 1.544 MPBS highways 14,18 are also known as DigitalSignal Level 1 lines (DS1) and are utilized to carry calls from thesubscriber lines 22, 24, 26, 28 to the switching system 12. Each DS1includes 24 individual 64 KBPS digital signal carrying facilities, whichare also known as Digital Signal Level 0 lines (DS0). For discussionpurposes, only one of the 24 DS0s is shown per each DS1.

The RDT 30 is utilized as an interface to assign and connect the DS0s tothe subscriber lines. The assignment and connection of the DS0s iseither accomplished on a per call basis or on a provisioned basis. Theper call basis is utilized when a large concentration of subscriberlines are required. This means that the RDT 30 has to dynamically assignand connect the DS0s to the subscriber lines. The subscriber linesutilizing a per call basis interface are known as concentrated lines24,26. While DS0s assigned and connected on a provisioned basis areknown as dedicated DS0s and the connected subscriber lines are known asnon-concentrated lines 22,28. The dedicated DS0s 16,20 are nailed upwhich means semi-permanently connected to the respective subscriberlines 22,28 at the RDT 30.

A problem with utilizing a provisioned type of interface is that thenon-concentrated subscriber lines 22,28 often lose access to thenetwork. Very often this is caused by a failed or blocked DS1, whichcauses the DS0s to become unavailable to the subscriber lines. This is aserious problem since the subscriber lines connected to the blocked DS1are unable to be utilized to make calls. The DS1s are often blocked dueto technical problems or maintenance purposes.

The above discussed problem is partially removed by incorporating DS1protection switching capability within the RDT 30. An example of a IDLCsystem having DS1 protection switching is shown in FIG. 2. In such asystem, a standby DS1 36 is reserved in the event one of the other DS1s32,34 fail or is blocked. When a DS1 fails, the traffic from that DS1 32is switched to the standby DS1 36 as shown in FIG. 3. Thus, the DS1protection switching partially solves the problem of a non-concentratedline losing access. However, the problem remains if a subsequent DS1 34fails before the previous failed DS1 32 is repaired as shown in FIG. 4.In this situation, the non-concentrated line 40 loses access. Thus, DS1protection switching is inadequate when there are consecutive DS1failures within a IDLC system.

It is therefore an object of the present invention to provide a devicewhich is capable of providing continual network access for subscriberlines even in the event of consecutive DS1 failures within a DigitalLoop Carrier System.

SUMMARY OF THE INVENTION

The aforementioned problems are obviated by the present invention whichprovides a device for enabling automatic restoration of network accessfor user lines within a communication system. The communication systemincludes said user lines interfaced with groups of transmission lines,each of said group of transmission lines including dedicatedtransmission lines which are connected to said user lines, idletransmission lines and reserved transmission lines. The device comprisesmeans for distributing said dedicated transmission lines among saidgroups of transmission lines and for continually providing a number ofsaid reserved transmission lines and means for identifying said userlines which have a dedicated transmission line in a group oftransmission lines that fails and then coupling each of said identifieduser lines to a respective available transmission line from the idle andthe reserved transmission lines.

The device may also include means for determining if a sufficient numberof said idle and reserved transmission lines are available and fordelaying coupling of said identified user lines if a sufficient numberof said idle and reserved transmission lines are not available. Thedevice may also include means for determining if a sufficient number ofsaid idle and reserved transmission lines are available and for delayingcoupling of an identified user line if an idle and reserved transmissionline is not available.

Advantageously, a device according to the present invention is operableto continually reprovision the non-concentrated subscriber lines of aDigital Loop Carrier system to the DS0s of the still functioning DS1s inthe event of a DS1 failure. Thus, the non-concentrated lines havecontinuous access to switched based services even if the DS1s carryingdedicated DS0s fail.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference is made to thefollowing description of an exemplary embodiment thereof, and to theaccompanying drawings, wherein:

FIG. 1 is a block diagram of an Integrated Digital Loop Carrier system;

FIG. 2 is a block diagram of an Integrated Digital Loop Carrier systemincorporating DS1 protection switching;

FIG. 3 is a block diagram of an Integrated Digital Loop Carrier systemincorporating DS1 protection switching exhibiting a DS1 failure;

FIG. 4 is a block diagram of an Integrated Digital Loop Carrier systemincorporating DS1 protection switching exhibiting consecutive DS1failures;

FIG. 5 is a block diagram of an Integrated Digital Loop Carrier systemaccording to the present invention;

FIG. 6 is a block diagram of an Integrated Digital Loop Carrier systemaccording to the present invention exhibiting a DS1 failure;

FIG. 7 is a block diagram of an Integrated Digital Loop Carrier systemaccording to the present invention exhibiting consecutive DS1 failures;

FIG. 8 is a block diagram of a distributed Integrated Digital LoopCarrier system according to the present invention;

FIG. 9 is a block diagram of a reprovisioning monitor according to thepresent invention;

FIG. 10 is a flow diagram of a repro reserve method according to thepresent invention;

FIG. 11 is a flow diagram of a method for determining the maximum numberof DS0s according to the present invention; and

FIGS. 12-24 are tables illustrating the operation of a repro reservemethod according to the present invention.

DETAILED DESCRIPTION

FIG. 5 illustrates an IDLC system according to the present invention.The IDLC system 60 has the same basic structure as the systems describedin the prior art except that it incorporates a reprovisioning monitorthat provides continual switch or network access for the subscriberlines. As can be seen from FIG. 5, the non-concentrated lines 38, 40 &44 are connected to respective transmission lines known as DigitalSignal Level 1s (DS1s) 32, 34 & 36, which carry the dedicated DigitalSignal Level 0s (DS0s).

In the event of a single DS1 failure as shown in FIG. 6, thenon-concentrated line 38 is reprovisioned 46 to another dedicated DS0contained in DS1 34. In the event of a consecutive failure as shown inFIG. 7, non-concentrated lines 38, 40 are both reprovisioned 48 to otherdedicated DS0s within DS1 36. The reprovisioning of the non-concentratedlines in both situations is controlled by the reprovisioning monitorimplemented in the IDLC system 60 according to the present invention.The specific details of the reprovisioning monitor are discussed below.

The operation of the reprovisioning monitor has a number of advantagesover DS1 protection switching. DS1 protection switching requires astandby DS1 to be reserved in case of a failure. In contrast, thereprovisioning monitor does not require an extra DS1 to be reservedwithin an IDLC system. This is because the reprovisioning isaccomplished by utilizing idle DS0s of other DS1s, which enables all ofthe DS1s to be utilized to carry traffic.

The reprovisioning monitor also eliminates the multiple switchingrequired by DS1 protection switching. In a system utilizing DS1protection switching, the traffic must be switched back from the failedDS1 when repaired in order to free up the standby DS1 in the case ofanother failure. In contrast, the reprovisioning monitor does notrequire the switching back of traffic. Moreover, the reprovisioning ofnon-concentrated lines does not depend on the failures of other DS1s.Therefore, the non-concentrated lines are capable of regaining networkaccess even when multiple DS1s fail.

Another advantage of the reprovisioning monitor is that thereprovisioning of non-concentrated lines does not depend on anyparticular DS1 which contains the idle DS0s. Thus, if necessary, theDS1s utilized to reprovision a particular non-concentrated line iscapable of being predetermined. This is beneficial in certaindistributed Digital Loop Carrier systems where the dedicated DS0s arerequired to be served by a pre-selected group of DS1s. For example, adistributed Digital Loop Carrier system may require that the DS0sdedicated to an ISDN BA line be served by the same interfacing unit orinterfacing unit portion.

Such a distributed system according to the present invention is shown inFIG. 8. The distributed IDLC system 58 includes an interface unit 60,DS1 groups 62,64,66 and a switching system 68, which functions similarlyas previously described for the IDLC system. In the distributed IDLCsystem 58, the subscriber lines are Integrated Service Digital Network(ISDN) lines 50,52. The ISDN lines 50, 52 are broadband communicationlines that allows the transmission of voice services along with othertypes of services such as video. The interface 60 has the capability ofseparating the respective two B and one D channels of ISDN lines 50, 52so that the ISDN data may be compatible with the rest of the network.

A reprovisioning monitor implemented in the distributed system 58enables the system to maintain a relationship between two or morededicated DS0s. In this case, the DS1s carrying the DS0s dedicated tothe B and D channels are required to be grouped together. As can beseen, the dedicated DS0s associated with the two B and one D channels ofISDN line 50 can be split into different DS1s of the first DS1 group 62.Similarly, the dedicated DS0s associated with the two B and one Dchannels of ISDN line 52 can be split into different DS1s of the secondDS1 group 64.

FIG. 9 shows a block diagram of the reprovisioning monitor according tothe present invention. The reprovisioning monitor 70 includes areprovisioning element 72, a monitoring element 74 and a DS0 managementelement 76, which are preferably implemented as additional softwarefunctions within the RDT or the switching system. The elements of thereprovisioning monitor 70 interface with the rest of the switchingsystem, which includes a fault analysis element 76, a call processor 78,a provisioning element 80 and a timing control 82.

When a DS1 fails or gets blocked during operation, the number ofnon-concentrated lines that have to be provisioned is dependent on thenumber of dedicated DS0s present on the failed DS1. In order to minimizethe number of new DS0s required to support this reprovisioning, the DS0management element 76 during normal operation attempts to distribute thededicated DS0s among all the DS0s serving the IDLC system (preferably,equally or substantially equally), while the non-concentrated lines areprovisioned by the provisioning element 80. The call processor 78provides information which enables the DS0 management element 76 toselect the DS0s to be distributed.

The DS0 management element 76 also reserves a certain number of DS0s byreducing the number of idle DS0s which are available to the concentratedlines. The reserved DS0s are utilized in order to reduce the situationswhere the reprovisioning process is deferred. The DS0 management element76 only reserves the minimum number of DS0s necessary to preventdeferment of the reprovisioning. This is accomplished by a repro reservemethod of the present invention which is invoked periodically by the DS0management element 76. The timing control 82 provides the timing forwhen a repro reserve method is invoked.

The DS0 management element 76 also provides a method for determining themaximum number of DS0s to be reserved to cover the failure of any oneDS1, which will be discussed in detail later.

The fault analysis element 76 is utilized to detect when a DS1 fails oris blocked in order to notify the reprovisioning element 72. In responseto this, the reprovisioning element 72 first identifies all thenon-concentrated lines which have dedicated DS0s on the failed DS1. Foreach identified non-concentrated line, the reprovisioning element 72clears the assignment of the dedicated DS0 from the failed DS1. Thereprovisioning element 72 then reprovisions or connects each identifiednon-concentrated line to an idle DS0 taken from one of the remainingDS1s by way of the DS0 management element 76. This reprovisioning onlyoccurs if there is an idle DS0 available at that time.

In order to determine if an idle DS0 is available, the monitoringelement 74 periodically communicates with the DS0 management element 76.The timing of this communication is controlled by the timing control 82.In the event an idle DS0 is not available, the monitoring element 74delays the reprovisioning until one is available. The monitoring element76 utilizes a polling technique to determine the availability of idleDS0s when the reprovisioning of a few non-concentrated lines arepending. Polling techniques are well known techniques utilized inmulti-point line configurations.

As discussed earlier, the DS0 management element 76 invokes a reproreserve method of the present invention in order to reserve the minimumnumber of DS0s necessary to prevent deferment of the reprovisioningprocess. In order to accomplish this, the repro reserve method operatesunder a number of rules and maintains a number of counts related to theIDLC system.

The counts maintained include the number of dedicated DS0s (F_(k)),number of reserved DS0s (R_(k)) and number of idle DS0s (I_(k)). Inregard to the above counts, the subscript K associates the counts to aparticular DS1. Also, let N identify the number of DS1s and M identifythe number of non-concentrated lines within the IDLC system. LetR_(total) identify the total number of reserved DS0s and F_(total)identify the total number of dedicated DS0s within the IDLC system. Itshould be noted that M is equal to F_(total). In order to understand therepro reserve method, let the DS1s identified with the numbers 1 to N sothat the associated F_(k) values are in descending order. In otherwords, F_(k) ≧F_(k+1).

The repro reserve method operates under the following rules. A DS0 canonly be reserved on a DS1 if the associated number of idle DS0s (I_(k))is greater than 1. Reserving a DS0 on a DS1 implies that the number ofreserved DS0s (R_(k)) is increased by 1. Also, each time a DS0 isreserved on a DS1, the associated number of idle DS0s on that DS1 isdecreased by 1. The last rule followed by the method requires that whena DS1 is selected in order to reserve a DS0, the DS1 that has the lowestF_(k) +R_(k) value is chosen.

The repro reserve method following the above last rule ensures that theDS0s are not reserved in excess. This is because when a DS1 fails or isblocked, the non-concentrated lines having the dedicated DS0s on thefailed DS1 are reprovisioned utilizing the DS0s reserved on theremaining DS1s. If r_(k) represents the excess number of reserved DS0sleft immediately after the completion of reprovisioning F_(k) number ofdedicated DS0s due to the failure of the DS1 numbered K(where 1≦K≦N),then

    F.sub.k +r.sub.k =R.sub.total -R.sub.k                     (1)

which is equivalent to

    F.sub.k +r.sub.k +R.sub.k =R.sub.total                     (2)

Let r_(total) identify the total number of excess reserved DS0s, byextending the above analysis to all the N DS1s. Since the goal of themethod is to reserve a minimum number of DS0s, r_(total) is expected tobe 0. This is equivalent to saying that each of the r_(k) values isexpected to be 0. This is because, ##EQU1## is only achieved when eachof the r_(j) s is 0.

When r_(k) =0,

    F.sub.k +r.sub.k =R.sub.total                              (4)

In other words, the goal of reserving a minimum of DS0s is achieved whenthe following conditions are met:

    F.sub.1 +r.sub.1 =R.sub.total and,                         (5)

    F.sub.2 +r.sub.2 =R.sub.total and,                         (6)

continuing . . .

    F.sub.N +r.sub.N =R.sub.total,                             (7)

which is equivalent to saying:

    F.sub.1 +r.sub.1 =F.sub.2 +r.sub.2 =. . . F.sub.k +r.sub.k =F.sub.N +r.sub.N(8)

In summarizing the above discussion, in order to reserve a minimum butsufficient number of DS0s the repro reserve method attempts todistribute the reserving of DS0s in such a way so that all of the DS1send up having the same F_(k) +r_(k) values.

FIG. 10 shows a flow diagram of a repro reserve method according to thepresent invention. Due to its periodic invocation, the method 84 startsout assuming it is being invoked for the first time. Thus, the basecounts of all of the DS1s associated with the IDLC system areinitialized to have 0 reserved DS0s 86, which means

For K=1 to N

    I.sub.k =I.sub.k +R.sub.k                                  (9)

R_(k) =0

Then the DS1 which has the highest number of dedicated DS0s isidentified 88. In this step, this particular DS1 is labeled by DS1_(max)and the number of dedicated DS0s this DS1 is associated with F_(max).Finding the DS1 with the highest number of dedicated DS0s is importantbecause this determines the minimum number of DS0s that are required tobe reserved in case of a failure. Since the number of DS0s reserved mustbe able to cover the failure of any one of the DS1s included in the IDLCsystem.

The method 84 next determines the number of idle DS0s the remaining DS1sare carrying 90 excluding DS1_(max). This step then associates thenumber of the idle DS0s with I_(remaining). Determining I_(remaining) isimportant because this enables the method to determine if additionalDS0s need to be reserved beyond I_(remaining). This is determinedindirectly by comparing I_(remaining) with F_(max) 92 to see ifI_(remaining) ≧F_(max). If this is true, T_(possible) is equated withF_(max) 94. If this is not true, T_(possible) is equated withI_(remaining) 94. Thus, T_(possible) is set to the smaller of eitherF_(max) or I_(remaining), which is utilized by the method 84 to reservethe proper number of DS0.

The method 84 then sets a variable count equal to T_(possible) 100. Thenext portion of the method 98 operates in a continuous loop to reservethe number of DS0s in the remaining DS1s that corresponds toT_(possible). This is accomplished by first checking to see if theCount=0 102, which enables the loop 98 to be broken. Initially thevariable count is not equal to 0 and then a DS1 is chosen which has boththe minimum F_(k) +R_(k) value and at least one idle DS0 104. Anadditional DS0 is then reserved in the chosen DS1 106. The variablecount is then decreased by one 108 and the method 84 loops back to whereit again checks to see if the count=0 102. The method 84 stays in theloop 98 until the count=0, which means that all of the T_(possible)number of DS0s have been reserved.

The above described loop 98 first reserves DS0s in DS1s having minimalF_(k) +R_(k) values, in order to evenly distribute the reservationprocess so that F_(k) +R_(k) values of all the DS1s are equal. This isdesirable because according to equation 8 such a condition ensures thatthe minimum necessary number of DS0s are reserved.

After the count=0, the DS1 is selected which has the maximum F_(k)+R_(k) value out of the remaining DS1s and designates this value by(F+R)_(max) 112. Then (F+R)_(max) is compared to F_(max) to see if(F+R)_(max) ≦T_(possible) 114. If this is true, a sufficient number ofDS0s have already been reserved to cover a failure of one of the DS1sand the method then exits 124. If this is not true, additional DS0s arerequired to be reserved in DS1_(max), which has the highest number ofdedicated DS0s.

The additional DS0s are reserved by first calculating (F+R)_(max)-T_(possible) 116, which is the number of additional DS0s that arerequired to be reserved. Then R_(max) is compared to I_(max) to see ifR_(max) ≦I_(max) 118, which determines if DS1_(max) has a sufficientnumber of idle DS0s to be reserved. If this is true, then the requirednumber of DS0s are reserved in DS1_(max) by setting I_(max) =I_(max)-R_(max) 122. If this is not true, the number of idle DS0s are increasedby setting R_(max) =I_(max) 120. Then the required number of DS0s arereserved in DS1_(max) by setting I_(max) =I_(max) -R_(max) 122. Afterperforming this step the method exits 124.

In regard to the method steps designated by numerals 112-122 of FIG. 10,the T_(possible) number of reserved DS0s are sufficient to cover thefailure of any one of the remaining DS1s excluding DS1_(max) only whenT_(possible) is greater than or equal to the F_(k) +R_(k) valuesassociated with those DS1s.

The DS0s reserved on a DS1 are not available when that particular DS1fails. In other words, the number of DS0s available to cover the failureof a DS1 numbered L (where 2≦L≦N) is equal to T_(possible) -R_(L). Thenumber of DS0s required when the DS1 numbered L fails is equal to thenumber of dedicated DS0s on that DS1 which is F_(L).

The T_(possible) -R_(L) number of reserved DS0s (i.e. reserved on theDS1s excluding the DSls numbered 1 and L) are sufficient enough to coverthe failure of the DS1 numbered L when T_(possible) -R_(L) is greaterthan or equal to F_(L). In other words, no additional DS0s are requiredto cover the failure of the DS1 numbered L when the following is true:

    T.sub.possible -R.sub.L ≧F.sub.L, or                (10)

    T.sub.possible ≧F.sub.L +R.sub.L                    (11)

In the event F_(L) >T_(possible) -R_(L), a few additional DS0s arerequired to cover the failure of the DS0 numbered L. This additionalnumber of reserved DS0s required is equal to F_(L) -(T_(possible)-R_(L)) or F_(L) +R_(L) -T_(possible).

Let P and Q identify two DS0s which have F_(k) +R_(k) values greaterthan T_(possible). The additional number of reserved DS0s required tocover the DS1 P is equal to F_(P) +R_(P) -T_(possible) and theadditional number of reserved DS0s required to cover the DS1 Q is equalto F_(Q) +R_(Q) -T_(possible). The additional reserved DS0s are mademutually available to one another when the reservation is made on a DS1which is different from those two. Generalizing this to the DS1 numbered2 to N, the desired DS1 where the additional number of DS0s have to bereserved is 1.

Accordingly, when F_(P) +R_(P) -T_(possible) number of DS0s are reservedon the DS1 numbered 1, these additionally reserved DS0s are available tocover the failure of the DS1 numbered Q. Therefore, the total number ofreserved DS0s available to cover the failure of the DS1 numbered Q isnow increased to:

    T.sub.possible -R.sub.Q +F.sub.P +R.sub.P -T.sub.possible, or (12)

    F.sub.P +R.sub.P -R.sub.Q.                                 (13)

Since F_(Q) identifies the total number of reserved DS0s required tocover the failure of the DS1 numbered Q, additional DS0s are notrequired if:

    F.sub.Q ≦F.sub.P +R.sub.P -R.sub.Q,                 (14)

which is equivalent to saying that additional DS0s are not required tobe reserved if:

    F.sub.Q +R.sub.Q ≦F.sub.P -R.sub.P.                 (15)

Therefore, by choosing the highest possible F_(k) +R_(k) value and byreserving the required (F+R)_(max) -T_(possible) number of DS0s on theDS1 numbered 1, all the remaining DS1s can be covered even if some otherDS1s have F_(k) +R_(k) values greater than T_(possible).

In summary, the method steps designated by the numerals 112-122 of FIG.10 determines the DS1 (from the DS1s 2 to N) which has the highest F_(k)+R_(k) value. Let (F+R)_(max) identify the corresponding F_(k) +R_(k)value. As illustrated above, no additional DS0s are required to coverthe failure of the associated DS1 as long as T_(possible) is greaterthan or equal to (F+R)_(max). When (F+R)_(max) is greater thanT_(possible), the additional number of reserved DS0s which are requiredto cover the failure of the DS1 associated with the (F+R)_(max) is equalto (F+R)_(max) -T_(possible). The method reserves (F+R)_(max)-T_(possible) number of DS0s on the DS1 numbered 1 (i.e., R₁=(F+R)_(max) -T_(possible)) provided enough idle DS0s are available onthat DS1. In other words, if (F+R)_(max) -T_(possible) is greater thanI₁ then the method reserves an I₁ number of DS0s on the DS1 numbered 1(i.e., R₁ =I₁).

The following are examples of the operation of a repro reserve methodaccording to the present invention.

EXAMPLE 1

N=3, F₁ =6, F₂ =5, F₃ =4.

First, 6 (which is F₁) DS0s are reserved on DS1s 2 and 3. Thereservation results in a R₂ =3, R₃ =3 or a R₂ =2, R₃ =4. In either case,the (F+R)_(max) value is 8. Since 8 is larger than 6 (which is F₁), R₁=(F+R)_(max) -F₁ =8-6=2.

When the DS1 numbered 1 fails, there are 6 reserved DS0s to cover the 6DS0s on the DS1s numbered 2 and 3. When the DS1 numbered 2 fails, thereare 6 or 5 reserved to cover the 5 DS0s on the DS1s numbered 1 and 3.When the DS1 numbered 3 fails, there are 4 or 5 to cover the 4 DS0s onthe DS1s numbered 1 and 2.

EXAMPLE 2

N=3, F₁ =7, F₂ =3, F₃ =2.

First, 7(which is F₁) DS0s are reserved on DS1s 2 and 3. The reservationresults in R₂ =3, R₃ =4. In this case, the (F+R)_(max) value is 6. Since6 is smaller than 7 which is F₁, no additional DS0s are required to bereserved on the DS1 numbered 1 or R₁ =0.

When the DS1 numbered 1 fails, there are 7 reserved DS0s to cover the 7DS0s on the DS1s numbered 2 and 3. When the DS1 numbered 2 fails, thereare 4 reserved DS0s to cover the 3 DS0s on the DS1 numbered 3 (note thatR₁ =0). When the DS1 numbered 3 fails, there are 3 reserved DS0s tocover the 2 DS0s on the DS1 numbered 2 (note that R₁ =0).

As noted above, the DS0 management element 76 also provides a method forcalculating the maximum number of DS0s which have to be reserved. In aDigital Loop Carrier system with N number of DS1s and M number ofnon-concentrated lines, the minimum number of DS0s which have to bereserved to cover the failure of any (but at most one at any instant oftime) of the DS1 is equal to M/(N-1) unless a single DS1 has morededicated DS0s than this. In the illustrations given below, it isassumed that enough idle DS0s are available to perform the reservation.

Let F₁, F₂, . . . , F_(N) identify the number of dedicated DS0s on theDS1s numbered 1, 2, . . . , N (i.e., F_(k) represents the number ofdedicated DS0s on the DS1 numbered K). Let F_(total) identify the totalnumber of dedicated DS0s within the IDLC system. It has to be noted thatF_(total) is equal to M. Let the DS1 numbers be identified in such a waythat the corresponding F_(k) values are in the descending order (i.e.,F_(k) ≧F_(k+1)).

Let R₁, R₂. . . , R_(N) identify the number of DS0s reserved on thoseDS1s numbered 1, 2, . . . , N (i.e., R_(k) represents the number of DS0sreserved on the DS1 numbered K). Let R_(total) identify the total numberof reserved DS0s within the IDLC system.

Let r₁, r₂, . . . , r_(N) identify the number of excessive DS0s leftimmediately after completing the reprovisioning process due to thefailure of one of the DS1s numbered 1, 2, . . . , N (i.e., r_(k)represents the number of excess DS0s left immediately after completingthe reprovisioning process due to the failure of the DS1 numbered K). Inother words, for K=1 to N,

    F.sub.K +r.sub.K =R.sub.total -R.sub.K, or                 (16)

    F.sub.K +R.sub.K =R.sub.total -r.sub.K.                    (17)

Utilizing equation 17 for all the DS1s, ##EQU2##

Based on the steps and rules of a repro reserve method,

    R.sub.total =F.sub.1 +R.sub.1                              (22)

Utilizing equation 22 within the equation 17,

    r.sub.1 =R.sub.total -(F.sub.1 +R.sub.1)=0                 (23)

Obviously, when R₁ =0,

    R.sub.total =F.sub.1                                       (24)

For R₁ >0,

    R.sub.1 =(F+R).sub.max -F.sub.1                            (25)

Therefore utilizing equation 22,

    R.sub.total =F.sub.1 +R.sub.1 =F.sub.1 +(F+R).sub.max -F.sub.1 =(F+R).sub.max                                            (26)

Then utilizing the equation 17, the r_(k) value for the DS1 associatedwith

    (F+R).sub.max is 0                                         (27)

Due to the rules and steps followed within a repro reserve method, theF_(k) +R_(k) values of any two DS1s can differ by at most 1. Based onequations 23 and 27 (i.e., at least two of the r_(k) values are 0),##EQU3## Based on equations 18 and 28,

    R.sub.total ≦(F.sub.total /(N-1))+((N-2))/(N-1)), or (29)

    R.sub.total ≦(F.sub.total /(N-1))+1-(1/(N-1))       (30)

Utilizing equations 19 and 30,

    (F.sub.total /(N-1))≦R.sub.total ≦(F.sub.total /(N-1))+1-(1/(N-11))                                      (31)

Since R_(total) represents the number of reserved DS0s, it has to be aninteger value. Utilizing equation 31, R_(total) has to be an integerwhich is greater than or equal to (F_(total) /(N-1)), but less than orequal to (F_(total) /(N-1))+1-(1/(N-1)). This is equivalent to saying:

    R.sub.total =Smallest integer≧(F.sub.total /(N-1))  (32)

In summary, utilizing equations 23 and 32, the maximum number of DS0swhich have to be reserved in an IDLC system with N number of DS1s and Mnumber of non-concentrated lines so as to allow the reprovisioningprocess to complete its task successfully, is the larger of thefollowing two values:

a) highest number of dedicated DS0s, a single DS1 has.

b) smallest integer≧M/(N-1).

FIG. 11 shows a flow diagram of the method for determining the maximumnumber of DS0s required according to the present invention. The method126 includes finding F_(max) 126, which is the DS1 that has the greatestnumber of dedicated DS0s. Then an integer value is calculated which is≧M/(N-1) 128, where M corresponds to the number of non-concentratedlines and N corresponds to the number of DS1s the system includes.Finally, F_(max) is compared to the integer value calculated in step 128in order to find the maximum value 130, which corresponds to the maximumnumber of DS0s which have to be reserved in case of a failure DS1 withinthe system.

The following are examples of the operation of the method described inFIG. 11.

EXAMPLE 1

N=3, F₁ =6₂, F₂ =5, F₃ =4.

M=6+5+4=15

Therefore, M/N(-1)=15/2=7.5

Since 6 (which is F₁) is smaller than 7.5, R_(total) has to be thesmallest integer greater than or equal to 7.5 In other words, themaximum numbers of DS0s which have to be reserved in this IDLC system isequal to 8.

EXAMPLE 2

N=3, F₁ =7, F₂ =3, F₃ =2.

M=7+3+2=12

Therefore, M/N-1=12/2=6

Since 7 (which is F₁) is greater than 6, R_(total) =7. In other words,the maximum number of DS0s which have to be reserved in this IDLC systemis equal to 7.

It should be specifically noted that the DS0s used during thereprovisioning process are not restricted to the DS0s reserved by arepro reserve method (as a matter of fact, the reprovisioning processneeds an idle DS0). This flexibility enables the reprovisioning monitorto encounter the situation of not having enough reserved DS0s (this canhappen if enough idle DS0s are not available when a repro reservedmethod is invoked) and complete its task of the reprovisioning process.

In the event the reprovisioning monitor is unable to find an idle DS0,the monitoring element defers the reprovisioning process until idle DS0sare available.

Additionally, it has to be noted that the reprovisioning monitor is ableto support multiple DS1 failures due to the fact that a repro reservemethod is invoked periodically and the monitoring element defers thereprovisioning process when idle DS0s are not available.

The following discussion relates to a model for demonstrating theoverall detailed operation of the reprovisioning monitor within aDigital Loop Carrier system according to the present invention. Themodel uses an IDLC system which has 200 subscriber lines with 5 DS1s andwhich serves 10% of the subscriber lines in a non-concentrated mode. Inother words, 20 subscriber lines have dedicated DS0s. Before a reproreserve method is invoked, the number of DS0s available to the 180concentrated lines is equal to 96 (it is assumed that out of 120 DS0s,20 are used as dedicated DS0s and 4 are used as the communicationchannels).

The model considers the failure of two DS1s (one after the another) andillustrates the management of DS1 based counts. Let the 5 DS1s beidentified using the symbols DS1₁, DS1₂, DS1₃, DS1₄, and DS1₅. Let usassume that DS1₁ contains the two communication channels (Time SlotManagement Channel (TMC) and Embedded Operations Channel (EOC). Further,let us assume that DS1₅ contains the backup of those two communicationchannels (referred to as TMC' and EOC'). Let I₁, I₂, I₃, I₄ and I₅identify the 5 DS1 based counts indicating the number of idle DS0s. LetF₁, F₂, F₃, F₄ and F₅ identify the 5 DS1 based counts indicating thenumber of dedicated DS0s. Let R₁, R₂, R₃, R₄, and R₅ identify the 5 DS1based counts indicating the number DS0s reserved by a repro reservemethod. While provisioning those 20 non-concentrated lines, the DS0management element 76 attempts to distribute the dedicated DS0s amongthe 5 DS1s, preferably equally. The repro reserve method of the presentinvention reserves the DS0s on the 5 DS1s to cover the failure of atmost one DS1. FIGS. 12-24 include tables that illustrate the DS1 basedcounts values of the model.

FIG. 12 illustrates the counts before provisioning the 20non-concentrated lines. FIG. 13 illustrates the counts afterprovisioning the 20 non-concentrated lines, but before reserving theDS0s (i.e., by the repro reserve method). FIG. 14 illustrates the countsafter reserving the DS0s. The number of DS0s reserved by the reproreserve method is the smallest integer≧20/4 which is equal to 5.

Now assume that one of the DS1s fail and let the failed DS1 be DS1₂. Thereprovisioning monitor reprovisions the 4 non-concentrated lines whichhave dedicated DS0s on the failed DS1. The repro reserve method,executed periodically, reserves the DS0s on the 4 DS1s to cover thefailure of at most one DS1. In this regard, FIG. 15 illustrates thecounts before reprovisioning the 4 non-concentrated lines. FIG. 16illustrates the counts after reprovisioning the 4 non-concentratedlines, but before the repro reserve method is invoked again. FIG. 17illustrates the counts after the repro reserve method is executed again.The number of DS0s reserved by the repro reserve method is the smallestinteger≧20/3 which is equal to 7.

Now assume that another DS1 fails and let the failed DS1 be DS1₃. Thereprovisioning monitor reprovisions the 5 non-concentrated lines whichhave dedicated DS0s on the failed DS1. The repro reserve method,executed periodically, reserves the DS0s on the 3 DS1s to cover thefailure of at most one DS1. FIG. 18 illustrates the counts beforereprovisioning the 4 non-concentrated lines. FIG. 19 illustrates thecounts after reprovisioning the 4 non-concentrated lines, but before therepro reserve method is invoked again. FIG. 20 illustrates the countsafter the repro reserve method is executed again. The number of DS0sreserved by the repro reserve method is the smallest integer≧20/2 whichis equal to 10.

Now assume that the failed DS1₂ is repaired. The DS1 based count valuesfor the reserved DS0s change due to the fact that the repro reservemethod is executed periodically. FIG. 21 illustrates the counts beforethe repro reserve method is executed again. FIG. 22 illustrates thecounts after the repro reserve method is executed again. The number ofDS0s reserved by the repro reserve method is the smallest integer≧20/3which is equal to 7.

Now assume that the failed DS1₃ is also repaired. The DS1 based countvalues for the reserved DS0s change due to the fact that the reproreserve method is executed periodically. FIG. 23 illustrates the countsbefore the repro reserve method is executed again. FIG. 24 illustratesthe counts after the repro reserve method is executed again. The numberof DS0s reserved by the repro reserve method is 7 since DS1₄ and DS1₅have more dedicated DS0s than the smallest integer≧20/4 (i.e., 5).

In summary, the above model illustrates that the non-concentrated linescontinue to have network access even when multiple DS1s fail. The reproreserve method, executed periodically, redistributes the reserved DS0sbased on the current distribution of other counts. For simplicity, thismodel deliberately neglected the call processing aspects (i.e., in termsof altering the I_(k) values) of concentrated lines. It has to be notedthat in some cases the DS1 based counts may be distributed among theDS1s in more than one way. For example, the distribution of R_(k) valuesin the last table can be reversed between DS1₂ and DS1₃ (i.e., the R_(k)value for the DS1₂ can be 4 and the R_(k) value for the DS1₃ can be 3).

The embodiments described herein are merely illustrative of theprinciples of the present invention. Various modifications may be madethereto by persons ordinarily skilled in the art, without departing fromthe scope or spirit of the invention.

What is claimed is:
 1. A device for enabling automatic restoration ofnetwork access for user lines within a communication system, saidcommunication system including said user lines interfaced with groups oftransmission lines, each of said group of transmission lines includingdedicated transmission lines which are connected to said user lines,idle transmission lines and reserved transmission lines,comprising:Means for distributing said dedicated transmission linesamong said groups of transmission lines, the means for distributingcomprising means for continually providing a number of said reservedtransmission lines; and Means for identifying said user lines which havea dedicated transmission line in a group of transmission lines thatfails, the means for identifying comprising means for coupling each ofsaid identified user lines to a respective available transmission linein another group from the idle and the reserved transmission linestherein.
 2. The device of claim 1, further comprising means fordetermining if a sufficient number of said idle and reservedtransmission lines are available and for delaying coupling of saididentified user lines if a sufficient number of said idle and reservedtransmission lines are not available.
 3. The device of claim 2, whereinthe means for determining comprises means for determining, via polling,the availability of a sufficient number of idle and reservedtransmission lines when said coupling of at least two identified userlines is not accomplished.
 4. The device of claim 1, further comprisingmeans for determining if a sufficient number of said idle and reservedtransmission lines are available and for delaying coupling of anidentified user line if an idle and reserved transmission line is notavailable.
 5. The device of claim 4, wherein the means for determiningcomprises means for determining, via polling, the availability of asufficient number of idle and reserved transmission lines when saidcoupling of at least two identified user lines is not accomplished. 6.The device of claim 1, wherein the means for distributingcomprises:means for determining which one of said groups of transmissionlines has the greatest number of dedicated transmission lines and forcounting the number of dedicated transmission lines in said group; meansfor counting the total number of idle transmission lines within saidother groups of transmission lines; means for comparing the number ofdedicated transmission lines in the group with the greatest number ofsaid lines to said total number of idle transmission lines in order todetermine a minimum number of idle transmission lines to be reserved;and means for reserving said minimum number of idle transmission lineswithin said other groups of transmission lines.
 7. The device of claim6, wherein the means for distributing further comprises means forreserving an additional number of idle transmission lines within thegroup of transmission lines having the greatest number of dedicatedtransmission lines if the number of dedicated transmission lines in saidgroup is less than said total number of idle transmission lines, saidadditional number of idle transmission lines corresponding to thedifference between the number of dedicated transmission lines in thegroup with the greatest number of said lines and said total number ofidle transmission lines.
 8. The device of claim 7, wherein the means forreserving an additional number of idle transmission lines comprisesmeans for comparing said minimum number of idle transmission lines tothe combination of dedicated transmission lines and reservedtransmission lines in the one of said other groups of transmission lineshaving the greatest combination of said lines.
 9. The device of claim 6,wherein the means for distributing further comprises means for initiallyreducing said reserved transmission lines of said groups of transmissionlines to zero.
 10. The device of claim 6, wherein the means forreserving said minimum number of idle transmission lines comprises meansfor continually reserving a single transmission line within said othergroups of transmission lines that have an idle transmission line and acertain minimum number of dedicated transmission lines and reservedtransmission lines.
 11. The device of claim 1, wherein the means fordistributing further comprises means for determining the maximum numberof said reserved transmission lines to be provided, which includes:meansfor determining which one of said groups of transmission lines has thegreatest number of dedicated transmission lines and for counting thenumber of dedicated transmission lines in said group; means forcalculating an integer value which is at least equal to the total numberof said user lines divided by one less than the total number of saidgroups of transmission lines; and means for comparing said integer valueto said number of dedicated transmission lines in order to determine amaximum number of idle transmission lines to be reserved.
 12. The deviceof claim 1, wherein the means for identifying comprises means forclearing the assignment to a respective identified user line of eachsaid dedicated transmission line in said group of transmission linesthat fails.
 13. The device of claim 1, wherein said communication systemis a Digital Loop Carrier system, said user lines are non-concentratedsubscriber lines, each said group of transmission lines is a DigitalSignal Level 1 line including a plurality of Digital Signal Level 0lines and said non-concentrated subscriber lines are interfaced withsaid Digital Signal Level 1 lines by a remote terminal.
 14. The deviceof claim 1, wherein said communication system is a distributed DigitalLoop Carrier system, said user lines are Integrated Service DigitalNetwork (ISDN) lines and said groups of transmission lines are groups ofDigital Signal Level 1 lines including a plurality of Digital SignalLevel 0 lines, the respective channels of an ISDN line being connectedto different Digital Signal Level 1 lines within the same group.
 15. Adevice for the assignment and connection of users to transmission lineswithin a communication system, comprising:means for apportioning usersexclusively coupled to respective transmission lines among groups oftransmission lines of the system; means for identifying each userexclusively coupled to a transmission line of a respective group oftransmission lines upon failure of the respective group;and means forre-coupling each identified user exclusively to an availabletransmission line of any other group of transmission lines.
 16. Thedevice of claim 15, further comprising means for reserving theavailability of a number of transmission lines among the groups oftransmission lines.
 17. The device of claim 16, wherein the means forreserving comprises means for determining the minimum number oftransmission lines to be reserved in each group of transmission linesupon the failure of any one of the other groups of transmission lines.18. The device of claim 16, wherein the means for reserving comprisesmeans for determining the maximum number of transmission lines to bereserved upon the failure of any one of the groups of transmissionlines.
 19. The device of claim 15, further comprising means for delayingthe re-coupling of an identified user until a transmission line ofanother group of transmission lines becomes available.
 20. The device ofclaim 19, wherein the means for delaying comprises means for polling theother groups of transmission lines for the availability of transmissionlines.
 21. The device of claim 15, further comprising means foridentifying transmission lines of other groups of transmission linesthat are available for re-coupling of an identified user; and means fordelaying the re-coupling of an identified user until a transmission lineof another group of transmission lines is identified as being available.22. The device of claim 21, wherein the means for identifyingtransmission lines comprises means for polling the other groups oftransmission lines for the availability of transmission lines.